Pruritic Dermatitis - Types, Causes, and Treatment.

Introduction

Pruritic dermatitis is a type of skin disease that appears to be painful and irritating and makes the patient scratch on a specific localized area or several areas of the body. Pruritus may be the symptom of an underlying skin condition, and most commonly it may be due to

• Allergens.

• Dry skin.

• Pregnancy.

• Body’s reaction to a medication.

Even pruritus may be chronic if itching persists for more than six weeks.

What Is Pruritus?

Pruritus is the medical term for an unpleasant sensation felt on the skin that makes the patient scratch or rub on the affected area. The itch may cause frustration or discomfort in severe cases, which may lead to,

• Disturbed sleep.

• Anxiety.

• Depression.

Constant scratching can damage the skin and reduce the effectiveness of one's major protective barrier.

What Are the Types of Pruritus?

The cause of itchiness is categorized into many types. Some common types of pruritus include:

• Brachioradial Pruritus - Upper arm itching caused by nerve damage.

• Nocturnal Pruritus - Itching during night time caused due to the body's reaction to a medication or contacting skin irritant.

• Pruritus Ani - Itching of skin around the anus may be caused by hemorrhoids (blood vessels in the rectum or anus become swollen) or skin infection, or some irritants.

• Senile Pruritus- Seen in people over 60 years of age which causes itching in the skin due to aging.

• Uremic Pruritus - Itching is seen as a symptom in people diagnosed with renal diseases who receive dialysis (a blood purifying process performed in a hospital set up in patients whose kidney function is compromised).

What Are the Cutaneous Signs of Pruritus?

There are no specific skin signs associated with pruritus other than scratch marks and signs of the underlying condition. Persistent scratching over some time can lead to:

• Lichenification (thickened skin, lichen simplex).

• Prurigo nodules (pink color firm nodules in the skin) and papules (raised, tender skin bumps).

Who Gets Pruritus?

Pruritus is most common, and it affects everyone during their lifetime. Severity and frequency vary according to each person. One may be at more risk of pruritus if one is,

• 65 years or more.

• Having allergies.

• Having underlying diseases like eczema (skin inflammation), psoriasis (a skin disease resulting in itchy and scaly dry patches), or diabetes (a metabolic condition that causes elevated blood sugar levels).

• Pregnant.

• On dialysis.

Mechanism Underlying Pruritus:

Itching and pain can originate anywhere along the neural pathway, from the central nervous system to the peripheral nervous system and the skin.

Mechanisms underlying pruritus are complex. Itch signal is transmitted mainly through small, itch-sensitive C-fibers in the skin in addition to histamine-triggered and non-histaminergic neurons.

What Causes Pruritus?

Causes of pruritus dermatitis can be classified under the following.

• Localized Pruritus: Localized pruritus is confined to a particular body part that occurs in forming a primary rash (e.g., dermatitis) or due to hypersensitive nerves in the skin (neuropathic pruritus). Neuropathic pruritus causes compression or degeneration of nerves on the skin, on the route of the spine, or in the spine itself. Neuropathic itch is sometimes associated with the absence or reduced sweating in the affected skin area.

Typical causes of localized itchy rashes:

1. Scalp: Seborrhoeic dermatitis caused by head lice.

2. Genitals: Vulvovaginal Candida albicans infection (vaginal infection caused by the fungus Candida), lichen sclerosus (a chronic disease condition causing white patches, specifically in the genital areas.

3. Hands: Pompholyx (a type of eczema that affects hands), irritant, and or allergic contact dermatitis.

4. Feet: Tinea pedis (fungal infection in the toes).

5. Back: Grover disease (A skin disorder associated with tiny, pink skin bumps).

6. Legs: Venous eczema.

Neuropathic causes of localized pruritus without primary rash (cutaneous dysaesthesia).

1. Face: Trigeminal trophic syndrome (an uncommon condition resulting due to damage to the trigeminal system.

2. Hand: Cheiralgia paresthetica (it is a sensory condition that results due to compression neuropathy).

3. Genital: Pruritus vulvae (an unpleasant condition caused by multiple dermatological changes in the female genitalia), pruritus ani (a skin condition affecting the perianal areas).

4. Arm: Brachioradial pruritus (a nerve disorder that causes itching, tingling sensation, and stinging in the outer part of the forearm).

5. Dermatomal: Herpes zoster (shingles) causes eczema during the recovery phase.

6. Back: Notalgia paresthetica (a chronic neuropathic condition seen in elderly females).

Systemic Causes of Pruritus: Systemic pruritus causes generalized pruritus called metabolic itch. Nothing is wrong with the skin until it gets scratched. Metabolic disorders include chronic renal failure and liver diseases.

1. Uremic pruritus arises in dialysis patients due to dry skin, peripheral neuropathy (nerve changes), and inflammation.

2. Once chronic pruritus has occurred, secondary changes that happen in the nerves in the skin and central nervous system may increase the sensation of itch.

3. Hepatogenic pruritus is more common in intrahepatic cholestasis. Examples of intrahepatic cholestasis are associated with

• Chronic viral hepatitis.

• Primary biliary cirrhosis.

• Pregnancy-related cholestasis.

Extrahepatic cholestasis is due to pressure on the bile ducts, e.g., from pancreatic tumors or pseudocysts.

1. Hematological disorders include iron deficiency anemia and polycythemia vera (one type of blood cancer).

2. Endocrine disorders include thyroid disease (hypo or hyperthyroid) and diabetes mellitus.

Paraneoplastic itch is associated with lymphoma (cancerous growth in the lymphatic system), especially Hodgkin lymphoma, leukemia (blood cancer), or solid organ tumor (for example, lung, colon, brain cancer). Infections causing itch are associated with human immunodeficiency virus infection (HIV) and hepatitis C.

Pruritus Skin Diseases: Pruritus is a symptom of many skin conditions. Some of them are included in the following list:

1. Dry Skin.

2. Lice.

3. Atopic dermatitis (an itchy skin inflammation).

4. Sunburn.

5. Allergic contact dermatitis.

6. Urticaria (skin rash).

7. Psoriasis.

8. Scabies (an itchy skin condition caused by burrowing mite and spreads easily to others).

9. Miliaria (a skin condition that results as a consequence of blocked sweat glands).

10. Pityriasis rosea (a skin rash generally arising in the chest as an oval spot).

11. Mycosis fungoides (a blood cancer type).

Exposed-Related Pruritus: Pruritus may arise due to exposure to certain external factors, such as the following

1. Allergens or irritants.

2. Cold, which can cause winter itching.

3. Inducible urticaria, such as dermographism (an urticarial eruption due to skin trauma or pressure on the skin).

4. Aquagenic pruritus (itch on exposure to water).

5. Insects and infestations, such as scabies.

6. Medications (topical or systemic), such as opioids and aspirin.

Hormonal Reasons for Pruritus: In pregnant women, about 2 % have pruritus without any dermatological cause. In some cases, cholestasis (bile pooling in the gallbladder and liver) causes itchiness. It usually occurs in the third trimester, and it gets relieved after giving birth. Generalized itch is also a common symptom of menopause.

How Is Pruritus Diagnosed?

The first steps in evaluating an itchy patient are medical history and examination. A healthcare provider should investigate patients who are without any primary skin lesions, and little evidence of chronic scratching may be a symptom of systemic, neuropathic, and psychogenic causes. Investigations lists include:

• Complete Blood Count - The parameters in the blood like red blood cells, white blood cells, platelets are checked to find any infection or abnormality.

• Creatinine and Renal Function Tests - These blood tests are done to check the functioning capacity on the kidneys .

• Liver Function Tests - These blood tests reveal the levels of liver enzymes like alanine transaminase, aspartate transaminase, alkaline phosphatase, etc. Any deviation from the normal levels suggests an infection or abnormality.

• Thyroid Function Tests - This blood test reveals the levels of thyroid hormones to figure out any thyroid disorders.

• Erythrocyte Sedimentation Rate - .This blood test reveals if there is any inflammation in the body.

• Chest Radiography - An X-ray of the chest is done to check for any abnormalities in the chest region..

• HIV Serology - This blood test is done to check the presence of HIV antigen and antibodies to figure out the immune response in accordance with HIV infection.

What Treatment Is Available for Pruritus?

Management of pruritus lies in removing the underlying cause of itching and to prevent further itching.

Topical Treatments:

• Wet dressings or showers to cool the skin.

• Using calamine lotion should be avoided on dry skin.

• Mild topical corticosteroids for short periods.

• Topical antihistamines must not be used for chronic itch.

Systemic Therapy: Oral medications may be necessary when pruritus is severe and in disturbed sleep. Some drugs may help in relieving itchiness.

• Antihistamines.

• Doxepin and Amitriptyline.

• Tetracyclic antidepressants.

• Antiepileptic drugs.

• Aspirin.

• Thalidomide.

• Rifampicin.

Phototherapy: Broad-band ultraviolet B (broadband ultraviolet B or UVB radiation, used for the treatment of moderate to severe psoriasis) or narrow-band UVB (narrow-band ultraviolet B (NB-UVB) type of light therapy used in the treatment of certain skin conditions, including psoriasis, mycosis, chronic dermatitis, and others). Phototherapy alone or in combination with UVA (ultraviolet A or UVA has a longer wavelength) has been shown to help where pruritus is associated with chronic kidney disease, psoriasis, atopic eczema, and cutaneous lymphoma.

Behavioral Therapy: Behavioral therapy is used with pharmacotherapy to modify behaviors such as stress reduction and helps interrupt the itch-scratch style cycle. Benefits are seen as reducing itch frequency and scratching.

Conclusion

Management of severe long-term itch is difficult and often requires combination therapy for an extended time. Treating underlying conditions causing itching may help in treating the disease. However, symptoms may quickly disappear with treatment or persist for a longer time if appropriate treatment was not initiated. However, with accurate treatment the condition can be resolved and will help improve the living condition of the patient.